PROJECT SUMMARY The overarching goal of this treatment project is to document the efficacy of very early transactional supports that parents can learn to change developmental trajectories and optimize outcomes of their child using a 2-stage sequential multiple assignment randomized trial (SMART) design to develop an adaptive intervention. All parent-infant dyads in the Emory ACE will be invited at 6 months of age from the pool of 250 high and low risk siblings and will be randomly assigned at Stage 1 to the Social Communication Growth Charts (SCGC) that uses an innovative web-based technology to teach parents early social communication milestones and how to support their child?s very early development or Usual Care to compare efficacy of the SCGC on parent contingent responsiveness and child developmental trajectories. Familes of children who show early signs of ASD at 12 months of age based on tailoring variables using parent report and observational measures will be re-randomized to Stage 2 to compare the efficacy of a parent-implemented (P-I) condition of a naturalistic developmental behavioral intervention (NDBI) based on the Early Social Interaction model1 to a clinician-implemented (C-I) condition NDBI based on a hybrid model from 12 to 21 months of age. Outcome measures of social communication, autism symptoms, social visual engagement, developmental level, and adaptive behavior will be gathered every 6 months from 6 to 30 months of age to measure treatment effects. Measures of parent transactional support and child active engagement will be collected quarterly from 9 to 30 months of age to examine growth trajectories during the Stage 1 and 2 conditions and at follow-up at 21 and 30 months after intervention. The expected impact of this study will have the following important implications: 1) maximize the use of technology to teach all parents how to support their infant?s development early to optimize opportunities for learning and recognize as early as possible if their child is not meeting developmental milestones and may need intervention; 2) document improved outcomes for very young children with early signs of ASD receiving a manualized, evidence-based NDBI intervention that is cost-efficient and feasible for community-based implementation; and 3) substantiate that these adaptive interventions implemented by parents beginning at 6 months of age lead to better child outcomes, providing evidence that very early detection of autism is crucial to improve developmental outcomes.